Fuel containment and recycling system

ABSTRACT

An energy conversion system, comprising: a reservoir container including at least two chambers of inversely variable volume for respectively storing a quantity of fuel and receiving a quantity of exhaust; a means for decreasing the volume of the first chamber while concurrently increasing the volume of the second chamber; at least one energy conversion device; first means for communicating fuel between the at least one energy conversion device and a first of the chambers in the reservoir container; and second means for communicating exhaust between the at least one energy conversion device and a second of the chambers in the reservoir container. The reservoir container may be transported to a recharging/refilling station or recharged in-situ. A particular application for metal-air fuel cell power systems is shown and described.

FIELD OF THE INVENTION

The present invention relates generally to fuel and exhaust containmentfor energy conversion systems, and more particularly, to fuel containersand recycling systems for metal-air fuel cells.

BACKGROUND OF THE INVENTION

Fuel cells, and in particular metal-air battery systems, have long beenconsidered a desirable power source in view of their inherent highenergy density. A fuel-cell battery includes a cathode, an ionic mediumand an anode. A metal-air cell employs an anode comprised of metalparticles that is fed into the cell and oxidized as the cell discharges.The cathode is generally comprised of a semipermeable membrane, a meshof inert conductor, and a catalyzed layer for reducing oxygen thatdiffuses through the membrane from outside the cell. Since oxygen isreadily available in the air, it is usually unnecessary to utilize adedicated oxygen storage vessel for the fuel-cell battery (except incertain configurations where there the oxygen supply is limited due todesign considerations). This makes metal-air cells very efficient onboth a volumetric energy density and cost basis. The cathode and anodeare separated by an insulative medium that is permeable to theelectrolyte. A zinc-air refuelable battery consumes zinc particles andoxygen as zinc is oxidized by the reaction with ions passing through theelectrolyte while liberating electrons to produce electricity. Thereaction products are generally comprised of dissolved zincate andparticles of zinc oxide suspended in the spent electrolyte.

Prior art metal-air systems have been demonstrated with sufficientenergy capacity to power electric vehicles. Such metal-air batterieshaving recirculating metal slurry anodes were built for demonstrationpurposes in the 1970s by Sony, Sanyo, the Bulgarian Academy of Sciences,and the Compagnie General d'Electricitie. These systems never achievedany commercial success because they all had relatively low power output(acceptable drain rates and overall capacities). Until now, this hasbeen the major obstacle to providing a commercially viable system. Forexample, Sony could only provide 24 W/kg, and Compagnie Generald'Electricitie was limited to 82 W/kg or 84 Wh/kg. The theoreticalcapacity, however, is well in excess of five times these valuesdepending upon the type of fuel utilized. One type of recent metal-aircell has realized an improvement in capacity by utilizing a packed bedof stationary anode particles and an electrolyte which moves through thebed without the use of an external electrolyte pump. Although thissystem has increased the cell capacity to about 200 W/kg with an energydensity of about 150 Wh/kg, further improvements are necessary beforecommercial success will be realized.

Metal-air refuelable batteries can be refueled in a short amount of time(i.e., minutes), compared to the several hours typically required torecharge conventional batteries. This characteristic makes them verywell suited to mobile applications such as electric vehicles, portablepower sources and the like. During the refueling operation, fresh anodemetal and electrolyte are added to the cell, and the reaction productsand spent electrolyte are removed. The reaction products must be eithertransported to an industrial facility for recycling or used, as is, foranother purpose. Several methods have been proposed for refuelingmetal-air cells. One known system employs two reservoirs, one to storefresh anode fuel and one to accommodate reaction materials from thecell.

U.S. Pat. No. 4,172,924 discloses a metal-air cell that utilizes a fluidmetal fuel comprised of a mixture of metal particles and liquidelectrolyte in a paste form. The paste moves from a first reservoirthrough the electrochemical battery where it is oxidized at acorresponding metal oxide paste cathode. The reaction products(primarily metal oxide) are communicated to a second reservoir. Whilethis arrangement increases the drain rate by removing the reactionmaterials, the multiple reservoir design wastes space, adds complexity,and increases cost.

Recently issued U.S. Pat. No. 5,952,117 discloses a fuel cell batterydesigned to overcome the disadvantages associated with the dualreservoir configuration described above. The '117 patent discloses atransportable container for supplying anode material and electrolyte tothe fuel cell battery, circulating electrolyte in a closed system, andcollecting spent anode reaction product. In accordance with theteachings of this patent, the container is first filled with zinc fuelparticles and fresh electrolyte. Next, the container is transported tothe fuel cell battery and connected to the battery such that it becomespart of the electrolyte flow circuit. After the zinc fuel andelectrolyte are used for a period of time during battery discharge, thecontainer, now containing at least partially spent electrolyte andreaction products, is removed from the battery and transported back tothe refilling apparatus. The contents of the container are subsequentlyemptied into the refilling apparatus and the process is repeated. Thespent electrolyte and reaction products are regenerated at a zincregeneration apparatus and then returned to the refilling apparatus.Although this arrangement obviates the need for two separate containers,the collection of reaction products can be made effectively only afterthe fuel supply has been exhausted and the container has been emptiedinto the refilling apparatus.

Another shortcoming of this system concerns the structure for preventingstray short circuit currents between a plurality of cells that are fedfuel in parallel. In that configuration, the cells are not electricallyisolated from each other through the conductive fuel feed. To preventshort-circuiting, the '117 patent discloses a filter for blocking largeparticles of anode material from passing through the conduits betweenthe fuel compartments. Although effective for the pellet-type fuelparticles disclosed in the patent, this expedient cannot block thepassage of the small anode particles that are found in a paste-like fuelsubstance.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a convenient, economical and environmentally safe fuel supplyand waste material retrieval system for use with an energy conversiondevice.

It is another object of the present invention to provide a singlereservoir container for concurrently supplying fuel to an energyconversion device and collecting exhaust from the energy conversiondevice.

It a further object of the present invention to provide a singlereservoir container for supplying fuel and collecting reaction products,respectively, to and from fuel cells, and in particular, metal-air fuelcells using zinc, aluminum, lithium, magnesium, silver, iron and thelike.

It is another object of the present invention to provide a metal-airfuel cell system that can be used for varied applications in terms ofpower requirements (i.e., in the watt to megawatt range). Suchapplications include, but are not limited to, providing energy forpowering motor vehicles, portable and consumer electronics, homes andindustry.

It is yet another object of the present invention to eliminateshort-circuiting between a plurality of electrochemical cells having asingle fuel feed.

In view of the above objects and additional objects that will becomeapparent hereinafter, the present invention generally provides a methodand system for providing fuel to an energy conversion device from asingle reservoir container and concurrently receiving exhaust from theenergy conversion device in the container.

In particular, the present invention provides a fuel cell system thatincludes a reservoir container, which is connectable to the cell tosupply fuel and concurrently collect waste or reaction materials thatare generated as the cell discharges. The invention is adapted for usewith hybrid rechargeable fuel cells, and in particular, metal-air fuelcell batteries having metal anode material in fluid form. The word“fluid” is defined herein as a paste-like substance such as for examplesmall particles of metal suspended in a fluid electrolyte, i:e., a KOHsolution and varying additives. Metal-air fuel cells operate as oxygenor air (fuel) oxidizes the metal anode as part of the electrochemicalcell reaction.

In the present invention, the fluid anode, particularly zinc-metal fuel,is supplied from a single reservoir to multiple cells in a batterysystem. During operation, as the cells discharge the resulting reactionproducts are continuously removed from the cells to the reservoircontainer and the cells are replenished with fresh anode fuel from thecontainer.

In accordance with a general aspect of the invention, there is provideda reservoir container for storing a quantity of fuel and a quantity ofexhaust in an energy conversion system having at least one energyconversion device. The reservoir container comprises a container bodyconnectable to the at least one energy conversion device and includes atleast two chambers of inversely variable volume disposed within thecontainer for respectively storing a quantity of fuel and receiving aquantity of exhaust. A structure is provided for decreasing the volumeof the first chamber while concurrently increasing the volume of thesecond chamber. During operation of the energy conversion device, fuelis supplied from the first of the chambers while exhaust is concurrentlyreceived in the second of the chambers. When the fuel supply isexhausted, the reservoir container may be removed and transported toanother location to enable regeneration of the exhaust into fresh fuel.The reservoir container is subsequently reconnected to the energyconversion device and fresh fuel is fed from what was previously the“exhaust” chamber while exhaust is received in the original fuel supplychamber.

In accordance with a particular implementation of the invention for afuel cell battery system, a single reservoir container is provided forstoring a quantity of electrochemical anode material and a quantity ofreaction products. The reservoir container includes at least twoisolated chambers of inversely variable volume, and at least one cellelement having a cathode and defining a volume for holding the anodematerial (metal and electrolyte) to form an electrochemical cell withthe cathode. A fluid delivery circuit communicates anode materialbetween the at least one cell element and a first of the chambers in thereservoir container. Either the same or an independent fluid deliverycircuit communicates reaction products between the cell(s) and a secondof the chambers in the reservoir container. In a preferred embodiment,the delivery circuit respectively comprises branch ducts or conduitsdisposed between the cell(s) and the reservoir container. Each conduitincludes an electrically insulating valve to selectively transfer freshanode material and reaction products to and from a single cell in agroup of cells which are electrically interconnected.

In accordance with another aspect of the invention, the fuel cell powersystem further comprises a subsystem for regenerating the reactionproducts into fresh electrochemical anode material after the reactionproducts are removed to the reservoir container from the cell(s); and astructure for varying the respective volumes of the first and secondchambers as fresh anode material is delivered to the cell and reactionproducts are delivered to the reservoir. The subsystem for regeneratingthe reaction products may be disposed proximal to the cells, or it canbe situated at a remote location and the reservoir container transportedthereto after all the fuel as been dispensed.

In another embodiment, the first chamber of the reservoir containercomprises a first subchamber for holding fresh anode material and asecond subchamber for holding electrolyte. These components aredelivered to a mixer from the respective first and second subchambersprior to communication to the cell(s). Likewise, the reservoir may beconfigured with a first subchamber for holding anode reaction materialand a second subchamber for holding used electrolyte. These componentsare separated from each other before they are delivered to the reservoirfrom the cell(s).

The invention further provides a method for supplying fuel to, andcollecting exhaust from, an energy conversion device. The methodcomprises the steps of:

connecting to the energy conversion device a reservoir container havingat least two chambers for respectively supplying a quantity of fuel toand receiving exhaust from the energy conversion device;

inversely varying the volume of the first and second of the chambers inthe reservoir to supply fuel to the energy conversion device and receiveexhaust from the energy conversion device;

disconnecting said container from said energy conversion device;

converting the exhaust into fuel within the container; and

reconnecting said container to the energy conversion device to supplyfresh fuel thereto from the second of the chambers and to receiveexhaust in the first of the chambers.

In a specific application of the above, the present invention provides amethod for supplying fuel to, and collecting reaction products from, atleast one fuel cell element, comprising the steps of:

connecting to the fuel cell a reservoir container having at least twochambers for respectively supplying anode fluid to and receivingreaction products from the fuel cell element;

inversely varying the volume of the first and second of the chambers insaid reservoir to supply anode fluid to the fuel cell and to receivereaction products from the fuel cell element;

disconnecting said container from the fuel cell;

converting the reaction products in the second of the chambers intofuel; and

reconnecting the container to said fuel cell to supply fresh anode fluidthereto from the second of the chambers and to receive reaction productsin the first of the chambers.

The present invention will now be described with particular reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an energy conversion system and singlereservoir container for supplying an energy conversion device andreceiving exhaust from the energy conversion device in accordance withthe present invention;

FIG. 2 is a schematic of a representative fuel cell power system inaccordance with the present invention;

FIG. 3 is a schematic of a modification of the embodiment shown in FIG.2 adding a dual-chambered mixing section to generate metal paste insitu;

FIG. 3A is a schematic of a reservoir having four sub-chambers and aseparator element for separating spent fuel into anode metal andelectrolyte;

FIG. 4 depicts a reservoir container having flexible walls to enable theanode material to be delivered by compressing the reservoir walls withhand pressure; and

FIG. 5 depicts another embodiment of a reservoir container having a handdriven piston mechanism for dispensing the anode material from thereservoir container.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The low energy density of typical metal air batteries has preventedtheir practical use in high rate applications such as, for example,powering motor vehicles. The present invention overcomes theshortcomings in the prior art by using a single reservoir container todispense the fuel and to collecting and reconsituting theelectrochemical reactants (i.e., mostly metal oxide)in a manner similarto secondary battery systems. The hybrid configuration (i.e.,refuelable/rechargeable) provides a long discharge life (or high energydensity), faster recharging capability leading to enhanced performanceduring discharge, and a longer cycle life.

The present invention embodies “fuel splitting” wherein multiplemetal/air cell voltages are obtained with only one fuel source withoutshort-circuiting the cells. As a result, batteries made with the cellconfiguration of the present invention can provide at least about 330Wh/kg/750 Wh/L, making them well suited as a power source for pure orhybrid electric vehicles.

In preferred embodiments of the invention, the air depolarized cathodesare designed to handle a discharging current density of 500 to 2000mA/cm² with an electrolyte capable of supporting a capacity of 5000Ah/L. It is preferred to utilize metal anode material comprisingcorrosion-resistant additives and alloys. The anode substance ispreferably comprised of small metal particles sized so that the metalparticles do not become completely oxidized on the anode surface duringthe electrochemical reaction. The preferred particulate range isselected to be between approximately 10 nanometers and one millimeter,although the smaller sizes provide higher capacity, better drain rate,and facilitate easier fluid transport through the system.

The metal fuel container is shaped to maximize the volumetric capacity,and to increase both capacity and discharge capability. With respect tothe shape of the individual cell elements, a cylindrical configurationis preferred for greater power density, although other shapes may beemployed within the scope of the invention.

The reservoir container includes a mechanical means for inverselyvarying the respective volumes of the fresh paste (fuel) storage chamberand the reaction products (exhaust) chamber as fresh metal paste flowsfrom the reservoir container and into the respective cells and the spentmetal paste returns from the cells to the reservoir container. Themechanical means may include a movable wall defining the boundarybetween the chambers such as a piston, screw mechanism and the like. Inthis manner, the reaction product occupies the space in which the freshmetal paste was previously disposed. The mechanical system can be usedto force the paste out of the container or it can operate in conjunctionwith external pumps in a fluid circuit.

For applications which have relatively smaller power requirements suchas consumer electronics, the reservoir can be designed with flexiblewalls that may be compressed by an external force (such as by a hand) toforce feed the fuel into the cells and to return the waste material tothe reservoir.

Where a plurality of cells are electrically interconnected, aninsulating/splitting system (ISS) may be employed to preventshort-circuiting. The ISS comprises a series of valves communicatingwith independent fuel feed lines that respectively join each cell. Thisconfiguration enables a single fuel reservoir to feed fresh metal pasteto a plurality of electrically isolated cells. The system utilizes an“on” and “off” mechanism which selectively enables fresh metal paste isfed into the individual cells as reaction materials are evacuated in the“on” state. During cell operation the ISS is turned off, and metal pastein each cell is electrically isolated from the main fuel pipeline.

In one embodiment, the ISS includes a Teflon (or some other insulatingmaterial) stopcock or valve positioned between each of the cells and themain feed pipeline. The stopcock/valve can be moved between left andright to open or close the paste pathway in a conventional manner. Inanother embodiment, the Teflon stopcock/valve can rotate through 90degrees to open or close the paste pathway. All of the stopcocks/valvesin the system move or rotate intermittently. As a result, the cells inseries are filled with fresh metal paste at the same rate, but in astaggered fashion. In this manner, the ISS prevents current leakage orshort-circuiting between the cells through the metal fuel feed.

To maximize the volumetric efficiency of the system, each cellpreferably has a cylindrical-shape and comprises an air-diffusioncathode, a separator, and a nickel-based current collector. Metal pasteis continuously filled into a predefined space between the separator andanode current collector. Examples of conductive polymer gel membraneseparator materials where anion- and cation- conducting membranes areformed are disclosed in co-pending U.S. appl. Ser. No. 09/259,068, filedFeb. 26, 1999, which is hereby incorporated by reference. The gelcomposition of the membrane contains the ionic species within itssolution phase such that the species behaves like a liquid electrolyte,while at the same time, the solid gel composition prevents the solutionphase from diffusing into the device. Such a membrane comprises, inpart, a support material or substrate, which is preferably a woven ornonwoven fabric, such as a polyolefin, polyvinyl alcohol, cellulose, ora polyamide such as nylon. More particularly, the polymer-based gel orfilm portion of the membrane includes an electrolyte in solution withthe polymerization product of a polymerization initiator and one or morewater-soluble ethylenically unsaturated amide or acid monomers,preferably methylenebisacrylamide, acrylamide, methacryclic acid,acrylic acid, 1-vinyl-2-pyrrodlidinone, or combinations thereof.Specifically, the separator comprises an ion-conducting polymer-basedsolid gel membrane comprising a support onto which a polymer-based gelhaving an ionic species is contained within a solution phase. Thepolymer-based gel comprises a polymerization product of one or moremonomers selected from the group of water soluble ethylenicallyunsaturated amides and acids, and a reinforcing element selected fromthe group of water soluble and water swellable polymers, wherein theionic species is added to one or more of the monomers, and thereinforcing element is added prior to polymerization. Other separatormaterials that can be used in the present invention are disclosed inco-pending U.S. application Ser. No. 09/482,126, filed Jan. 11, 2000,the disclosure of which is hereby incorporated by reference. The '126Application discloses a separator comprising a support or substrate anda polymeric gel composition having an ionic species contained in asolution phase thereof. In preparing the separator, the ionic species isadded to a monomer solution prior to polymerization and remains embeddedin the resulting polymer gel after polymerization. The ionic speciesbehaves like a liquid electrolyte, while at the same time, thepolymer-based solid gel membrane provides a smooth impenetrable surfacethat allows the exchange of ions for both discharging and charging ofthe cell. Advantageously, the separator reduces dendrite penetration andprevents the diffusion of reaction products such as metal oxide toremaining parts of the cell. Furthermore, the measured ionicconductivity of the separator is much higher than such property of priorart solid electrolytes or electroyte-polymer films.

A suitable cathode structure is described in co-pending U.S. appl. Ser.No. 09/415,449, filed Oct. 8, 1999, the disclosure of which is herebyincorporated by reference. The cathode in the '449 Application comprisesa porous metal foam substrate, formed with a network of interconnectedpores. An active layer and a hydrophobic microporous gas diffusion layerare both disposed on one or more surfaces of the metal foam substrate.The metal foam substrate serves as the current collector of the cathode.The microporous layer is a plastic material such as a fluoropolymer(i.e., PTFE). The cathode may also include a particulate microstructurereinforced by relatively strong bonding provided by sintering apolymeric binder within the three-dimensional interconnected porosity ofthe metal foam substrate. The reactive layers are preferably fabricatedfrom the same material as binder. This advantageously enables a singleroll pressing operation to simultaneously impregnate the binder into thesubstrate and form the reactive layers thereon. A method for formingsuch an electrode may comprise the steps of mixing carbon with apolymeric binder to form a carbon/polymer blend, preparing thecarbon/polymer blend as a liquid dispersion or slurry, disposing thecarbon/polymer blend within the pores of the substrate in asubstantially continuous process, disposing an active layer on thesubstrate, and sintering the polymeric binder in-situ with the pores ofa current collector.

For the anode current collector, an integrated static mixer and currentcollector is used to efficiently mix the metal paste to constantlyexpose unreacted metal to the cathode surface while the fuel istravelling through a cell or power stack. This static mixer ensures goodcontact between the cathode and metal paste anode to optimize dischargecapability.

A preferred metal paste exhibits high electrochemical activity, goodfluidity, low internal resistance, and anti-corrosion property. Adesired paste composition consists of metal powder (or metal particlesin the aforementioned size range), fluid gel or paste formingelectrolyte (e.g. with about 30-35% KOH solution), anti-corrosion agent,lubricant, and electrical conducting agent and, if desired or necessary,other additives.

A fluid paste consisting of metal granules (which can be obtained from,for example, Aldrich Chemical Co., Milwaukee, Wis.), and 35% gelelectrolyte (5% polyacrylamide, 35% KOH, 60% water) exhibits desirablecharacteristics including low internal resistance and good fluidity.

With reference now to FIG. 1 of the drawings, there is depictedschematic overview of an energy conversion system 10 comprising anenergy conversion device 12, reservoir container 14, and fluid circuitgenerally denoted by the reference numeral 16. The energy conversiondevice 12 converts fuel into energy and exhaust, and can be any one of avariety of devices, with an illustrative application for a fuel cell(s)described in greater detail hereinbelow. The reservoir container 14 ispartitioned into at least two chambers 18a, 18b, for respectivelyholding varying quantities of fuel and exhaust. In this regard, thechambers 18 a, 18 b are adapted to vary inversely in volume such that asfuel is first dispensed from chamber 18a, an amount of exhaust iscollected in chamber 18 b. After the entire quantity of fuel fromchamber 18 a has been supplied to the energy conversion device 12 andchamber 18 b has filled with exhaust, the reservoir container can bedisconnected from the fluid circuit 18 by through appropriate fittingsdesignated generally at 20 a, 20 b. The reservoir container may then betransported to a facility/apparatus generally denoted at 27 forreconstituting the exhaust into fresh fuel using known processingtechniques, or for smaller scale applications in the case of a fuel cellbattery as described below, directly recharged by an apparatus in situ.The reservoir container 14, now containing a fresh supply of fuel inchamber 18 b (with chamber 18 a empty), is reconnected to the fluidcircuit 16 and the process of fueling the energy conversion device isreversed. Fresh fuel is then dispensed from chamber 18 b and the exhaustcollected in chamber 18 a. The entire process is thereafter repeated.

The reservoir container 14 depicted in FIG. 1 is schematically depictedwith a movable wall 22 that defines the boundary between the respectivechambers 18 a, 18 b and which varies the respective volumes of thechambers. The wall 22 may include a separate sealing assembly 24 (i.e.,an o-ring assembly) to prevent leakage between the chambers. The wall 22may be bi-directionally driven via a mechanical mechanism (not shown)operably coupled to a piston, screw-drive, or the like. It isanticipated that many expedients can be utilized, and those of ordinaryskill in the art will understand that the particular examples shownherein are not intended to be limiting.

The flow circuit 16 is schematically depicted as including a pair ofpumps 26 a, 26 b communicating with branch ducts, conduits, or pipesshown in solid and dotted lines. A pair of valves 28 a, 28 b may beindependently actuated to selectively enable fluid in the circuit toflow to and from each chamber. The dotted lines indicate pathways forreverse flow depending on the operation of the respective pumps 26 a, 26b when the fuel is either dispensed from chamber 18 a or chamber 18 b,and the exhaust is returned to the opposite chamber 18 b or 18 a. Theflow circuit 16 may further include one or more vents and associatedhardware of the type well known in the art of fluid plumbing.

These components are not shown for clarity and are well understood bythose skilled in the art.

Referring now to FIG. 2, there is shown a schematic of a representativefuel cell power system 30 in a first embodiment.

The power system 30 generally includes a reservoir container 32, powerstack 34, flow circuit 36 and valve/insulating system (ISS) 38. Thereservoir container includes a pair of chambers 40 a, 40 b of inverselyvariable volume as described above with respect to the generalembodiment illustrated in FIG. 1. As shown in FIG. 2, fluid anodematerial is initially contained in chamber 40 a. The flow circuit 36contains a pump 42 (a single pump is depicted, but more than one may beinstalled, with the additional pump(s) located proximal to chamber 40 a)to drive the fluid through the system. The fuel is initially dispensedfrom chamber 40 a to the ISS 38. The ISS 38 includes a fuel feed conduit44 having respective branch lines 46 a-d to communicate the anode paste(or reaction products upon reversal of the cycle) from the reservoircontainer 32 to a plurality of corresponding cell elements 48 a-d. Eachcell includes an air-cathode assembly 49 of the exemplary type describedabove. A similar conduit 50 with respective branch lines 52 a-d isconnected to the reservoir container 32 via the pump 42. The cellelements forming the power stack are electrically interconnected in aconventional fashion and communicate with an external application viaterminals 53 a, 53 b. During operation in an exemplary cycle, fuel istransferred from chamber 40 a and reaction products are communicatedfrom cell elements 48 a-d to the chamber 40 b. By moving a partition 54in the reservoir container 32 by a specific distance, the storage volumefor the reaction products in the reservoir chamber 40 b increases whilethe storage volume for anode fluid in chamber 40 a decreases (with a 20%volume compensation to account for the volume change as the fresh fuelis converted to reaction products). After the fuel is depleted, thereservoir container 32 is then transported to a recharging station(shown schematically in FIG. 1) for recharging/reconstituting thereaction products into fresh anode material. Alternatively, the wasteproducts may be recharged in-situ by applying a voltage to the oxidizedmaterial in a manner well known in the art. After charging, thereservoir container 32 is reconnected to the system and the cycle isreversed with the fresh anode fuel being dispensed from chamber 40 b andthe reaction products collected in chamber 40 a.

The corresponding valves 46 a-d and 52 a-d, respectively, operate inpairs to selectively feed fuel and exhaust reaction products to thecells. The inlet and outlet valves for contiguous cells operateindependently of each other, such that only a single cell at a time issupplied with fuel and exhausted of reaction products. As a result,there is no electrical continuity between the individual cells via theconductive metal anode material in the supply/removal circuit. This celldesign has few moving parts and simple construction with readilyavailable materials. The fuel, which is in the form of a paste comprisedof particles of metal and gel electrolyte as described above, can flowfreely through the system under pressure from an external pump, in amanner similar to hydrogen fuel in O₂—H₂ fuel cells. The integration ofthe fuel supply and waste material storage in a single containerpartitioned into inversely variable storage volumes for the respectivecomponents provides better space utilization, simplifies storage, supplyand transportation of the fuel, and ultimately provides consumers withreduced energy costs.

Referring now to FIG. 3, there is depicted another embodiment of ametal-air fuel cell power system 30′ with like components from the aboveembodiment similarly numbered. The fuel cell power system 30′ includes areservoir container 32′, power stack 34, flow circuit 36′ andvalve/insulating system (ISS) 38. The reservoir container has beenmodified to include a plurality of chambers 56 a, 56 b and 58. Chambers56 a and 56 b are driven together and vary in volume inversely tochamber 58 in accordance with the principles discussed above. The fluidanode metal here is separated from the electrolyte, with the metalinitially contained in chamber 56 a, and the electrolyte in chamber 56b. The flow circuit 36 contains pumps 42 a, to drive the fluid throughthe system. A mixer 58 communicates with the respective chambers 56 a,56 b to mix the fluid metal and electrolyte into “anode paste” prior tocell delivery via pump 42 b and fuel feed conduit 44. A plurality ofrespective branch lines 46 a-d communicate anode paste from thereservoir container 32 to a plurality of corresponding cell elements 48a-d. A similar conduit 50 with respective branch lines 52 a-d isconnected to the reservoir container 32′ via the pump 42 a. The cellelements forming the power stack are electrically interconnected in aconventional fashion and communicate with an external application viaterminals 53 a, 53 b. During operation anode metal and electrolyte aretransferred from chambers 56 a, 56 b, respectively, combined in themixer 58, and delivered to the cells 48 a-d. As the cells discharge, thereaction products are communicated to chamber 50. By moving a partition54 in the reservoir container 32′ by a specific distance, the storagevolume for the reaction products in the reservoir chamber 58 increaseswhile the storage volumes for fuel components in chambers 56 a, 56 bdecrease (with a 20% volume compensation). The reaction products fillthe full volume of the reservoir container 32′ after fuel depletion. Thereservoir container 32′ is then transported to a recharging station asdiscussed above. This configuration reduces the likelihood of corrosionby keeping the metal and electrolyte separated until the fuel is to beutilized in the cells.

In a modification of the foregoing as shown in FIG. 3A, chamber 58 ofreservoir chamber 32′ can be partitioned into subchambers 58 a, 58 b anda separator element 60 can be provided between the reservoir container32′ and conduit 50. The anode metal and electrolyte waste products areseparated into individual anode metal and electrolyte components by theseparator element 60 and then respectively stored in subchambers 58 a,58 b. These chambers are analogous to metal and electrolyte supplychambers 56 a, 56 b described above. In this manner, the metal oxide inchamber 58 a is reduced to fresh metal and the electrolyte isreconstituted or replaced in chamber 58 b. The operating cycle isthereafter reversed as described above.

Referring now to FIG. 4, there is depicted a reservoir container 62 foruse with consumer electronics such as household appliances and the like.The reservoir container 62 comprises a flexible vessel (i.e., plastic)and a fixed partition 64 defining a first chamber 66 a and a secondchamber 66 b for respectively storing anode material and receivingreaction products. In this embodiment pressure applied to the walls ofthe vessel will force-feed the anode material from the storage chamber66 a and through the conduit 68 to the electrochemical cell(s) (notshown). The reaction products are returned to chamber 66 b through asecond conduit 70. This “compressible” reservoir container is designedwith walls of sufficient thickness and having elastic propertiessufficient to permit hand pressure on the walls of the reservoircontainer to “squeeze out” a volume of fuel from the reservoircontainer. Although a person's hand is schematically depicted in thedrawing, it is anticipated that an external compressing device may beutilized. A preferred expedient will apply radial pressure to thereservoir wall in a “squeezing action” to uniformly dispense the fuel.

Referring now to FIG. 5, there is depicted another embodiment of areservoir container 72 comprising a body 74, and plunger 76. The plunger76 includes a piston 78 having a sealing assembly 79 and definingchambers 80 a, 80 b of inversely variable volume to provide thefunctionality discussed in detail above. A pair of conduits 82, 84respectively communicate with chambers 80 a, 80 b. The plunger 76includes an elongated hollow body 86 and a handle portion 88 tofacilitate grasping thereof. The conduit 84 passes through the hollowbody 86 and joins chamber 80 b as shown. When the plunger 76 is advancedto the left as shown in the drawing, the volume of chamber 80 a isreduced while the volume of chamber 80 b is concurrently increasedthereby forcing fresh fuel out of chamber 80 a and permitting reactionproducts or waste to be received in chamber 80 b.

It is to be understood that the foregoing drawings and description ofthe invention are merely illustrative, and it is anticipated thatobvious modifications will be made therefrom by those skilled in theart, without departing from the scope of the invention as defined in theappended claims. Although examples are shown and described for metal aircells and batteries, the single reservoir container of the presentinvention is well suited to any energy conversion device requiringcollection and storage of waste or reaction products.

We claim:
 1. A fuel cell system comprising: at least one fuel cellelement including a cathode; a reservoir container including at leasttwo chambers of inversely variable volume for respectively storing aquantity of fuel and receiving a quantity of exhaust, said reservoircontainer adapted for storing a quantity of electrochemical anodematerial and a quantity of reaction products, wherein said first chambercomprises a first subchamber for holding fresh anode material and asecond subchamber for holding electrolyte for the at least one fuel cellelement, and said system further includes means for mixing fresh anodeand electrolyte material from the respective first and secondsubchambers prior to communication to the at least one fuel cellelement; means for decreasing the volume of said first chamber whileconcurrently increasing the volume of said second chamber; first meansfor communicating fuel between said at least one fuel cell element and afirst of said chambers in said reservoir container; and second means forcommunicating exhaust between said at least one fuel cell element and asecond of said chambers in said reservoir container.
 2. The fuel cellelement of claim 1, further comprising: means for regenerating thereaction products into fresh electrochemical anode material in saidreservoir container; and means for varying the respective volumes ofsaid first and second chambers as fresh anode material is delivered tosaid fuel cell element and reaction products are delivered to saidreservoir.
 3. The fuel cell element of claim 1, wherein said first meansfor communicating and said second means for communicating respectivelycomprise at least one conduit coupling said at least one fuel cellelement to said reservoir, each conduit including electricallyinsulative valves to selectively enable communication of fresh anodematerial and reaction products to and from a single fuel cell element ina group of electrically interconnected cell elements.
 4. The fuel cellclement of claim 1, wherein said second chamber comprises a firstsubchamber for holding anode reaction material and a second subchamberfor holding used electrolyte, and said system further comprises meansfor separating the anode reaction material from the used electrolyte. 5.The fuel cell element of claim 1 wherein said anode material comprisesmetal, and said cathode includes an air depolarizer element.
 6. The fuelcell element of claim 5 wherein said material derived from said meansfor mixing fresh anode and electrolyte material from the respectivefirst and second subchambers is a fluid paste comprised of 65% metal 10granules by weight, and 35% gel electrolyte by weight.
 7. The fuel cellelement of claim 6, wherein said gel electrolyte comprises up to 5%polyacrylamide, 35% KOH, and water.
 8. The fuel cell element of claim 6,wherein said cathode is enclosed in a gelled separator element.
 9. Thefuel cell element of claim 1, wherein said cathode comprises a metalfoam substrate having an active layer, and a hydrophobic microporous gasdiffusion layer disposed on at least one surface of the metal foamsubstrate.
 10. For use in an energy conversion system having at leastone energy conversion device, a reservoir container for storing aquantity of fuel and a quantity of exhaust, the reservoir containercomprising: a container body connectable to the at least one energyconversion device and including at least two chambers of inverselyvariable volume disposed within said container body for respectivelystoring a quantity of fuel and receiving a quantity of exhaust; andmeans for decreasing the volume of said first chamber while concurrentlyincreasing the volume of said second chamber, wherein said reservoir hasat least one flexible wall and the system includes means for compressingthe flexible wall to force anode material out of said reservoir and intothe at least one fuel cell element.
 11. In an energy conversion system,a method for supplying fuel to, and collecting exhaust from, an energyconversion device, comprising the steps of: connecting to the energyconversion device a reservoir container having at least two chambers forrespectively supplying a quantity of fuel to and receiving exhaust fromthe energy conversion device; inversely varying the volume of the firstand second of said chambers in said reservoir to supply fuel to saidenergy conversion device and receive exhaust from said energy conversiondevice; disconnecting said container from said energy conversion device;converting the exhaust into fuel within said container; and reconnectingsaid container to said energy conversion device to supply fresh fuelthereto from the second of said chambers and to receive exhaust in thefirst of said chambers.
 12. In a fuel cell power system, a method forsupplying fuel to, and collecting reaction products from, at least onefuel cell element, comprising the steps of: connecting to the fuel cella reservoir container having least two chambers for respectivelysupplying anode fluid to and receiving reaction products from the fuelcell element; inversely varying the volume of the first and second ofsaid chambers in said reservoir to supply anode fluid to said fuel celland to receive reaction products from said fuel cell element;disconnecting said container from said fuel cell; converting thereaction products in the second of said chambers into fuel; andreconnecting said container to said fuel cell to supply fresh anodefluid thereto from the second of said chambers and to receive reactionproducts in the first of said chambers.